<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <form action="" method="POST">
       请输入你的分数：<input type="text" name="score">
       <input type="submit" name="submit" value="提交">
    </form>
    <h1>
        <?php 
        if(!empty($_POST['score']))
        {    
            $score = $_POST['score'];
            if(is_numeric($score))
            {
                if($score>=90)
                {
                    echo "优秀";
                }else if($score>=80&&$score<90)
                {
                    echo "良好";
                }else if($score>=60&&$score<80)
                {
                    echo "及格";
                }else
                {
                    echo "不及格";
                }
            }else
            {
                echo "成绩应该为数字";
            }
           
            
        }else
        {
           echo "请输入分数";
        }
        ?>
    </h1>    
</body>
</html>